Nitroguanidine is used as a propellant and explosive. It has a greater detonation velocity and higher inherent density than that of trinitrotoluene (TNT), yet it is relatively impact insensitive. This combination of properties makes nitroguanidine an important material. Unfortunately, when nitroguanidine is crystallized from aqueous solutions during preparation and purification, it forms as long needles and has a resultant bulk density of only about 200 to 300 grams per liter (g/1). This is referred to as low bulk density nitroguanidine. While these long needles can be pulverized by grinding, the bulk density is not greatly increased by such mechanical processing.
U.S. Pat. No. 4,544,769 describes a process of preparing compact or high bulk density nitroguanidine by recrystallization from an initially hot nitroguanidine solution, wherein the solvent for the nitroguanidine is selected from the group of: (i) polyhydric, lower aliphatic alcohols; (ii) mono- or dialkyl ethers of polyhydric, lower aliphatic alcohols; (iii) dimethylformamide; (iv) dimethyl sulfoxide; and, (v) mixtures thereof. The disclosure indicates that bulk densities of from 900 to 1020 g/1 are obtained in this process. However, repeated efforts by the present inventors to duplicate these results failed leading them to seek an alternative method of preparing high bulk density nitroguanidine from low bulk density nitroguanidine.
Accordingly, it is an object of this invention to provide a process of preparing spherical high bulk density nitroguanidine having a density of from about 900 to 1100 g/1 from low bulk density nitroguanidine.